Exhaust Hood

ABSTRACT

An exhaust hood having a first fan wheel sucking in and transporting away room air. A second fan wheel sucks in external air and is arranged axially displaced relative to the first fan wheel. Guide vanes are arranged externally about the first and second fan wheels. The guide vanes are embodied as a cavity and form venting passages. A first air flow exiting from the first fan wheel and a second air flow exiting from the second fan wheel are guided past each other, separate from each other, through the guide vanes and are directionally deflected by the guide vanes. Walls of the guide vanes form a surface for heat exchange between the first and second air flows.

The present invention concerns an exhaust hood with a first fan wheel for sucking in and transporting away room air and a number of guide vanes arranged externally about the fan wheel for directional deflection of the airflow that is exiting from the first fan wheel.

An exhaust hood of the aforementioned kind is disclosed in the publication DE 10 2007 051 942.9. As a result of the special arrangement and design of the guide vanes, it is possible to effectively precipitate from the sucked-in room air suspended particles, such as oils and grease, that are contained in the room air onto the guide vanes. However, because of the high air throughput through the exhaust hoods significant energy quantities are lost with the heated or cooled room air.

The publication DE 10 2005 033 224 A1 discloses the use of a heat exchanger in an exhaust hood. The heat exchanger is used in order to either heat cold air coming in from the exterior by means of the outflowing warmer room air in order to avoid heat losses or the cooled room air that is blown out to the exterior is used in order to cool the incoming hot air to the lower room temperature. Both applications serve to reduce energy losses from the building that are caused by venting.

In this known exhaust hood it is however to be seen as a disadvantage that the surfaces available for the heat exchange are limited and therefore only a minimal heat exchange is achieved. The heat exchange potential in the area of the exhaust hood is therefore not completely utilized. Moreover, the fan wheels and the venting passages are only accessible with difficultly. This is a disadvantage in connection with exhaust hoods because in the venting passages oil or grease particles are deposited that are unhygienic and may lead to odor nuisance or fire risks.

It is an object of the present invention to modify the aforementioned exhaust hood in such a way that energy losses due to blown-out room air can be reduced.

The object is solved for an exhaust hood of the aforementioned kind in that in the exhaust hood a second fan wheel for sucking in external air is arranged axially displaced relative to the first fan wheel and the air flows that are exiting from the first and second fan wheels are guided past each other, separate from each other, through guide vanes that are embodied as a cavity and form venting passages, wherein the walls of the guide vanes each form a surface for heat exchange between the two air flows.

By cross-over guiding of the air flows in the exhaust hood a heat exchange is enabled. Since a plurality of guide vanes within the exhaust hood are provided in order to obtain a high degree of separation, the surfaces of these guide vanes together also form a large surface area by means of which a heat exchange can be realized. Because of the comparatively high flow velocity of the room air through the exhaust hood and the usually short transport paths of the room air from the exhaust hood to the exit opening in a building wall, the heat exchange that is generally possible in conventional exhaust hoods is very limited. By utilizing the surfaces of the guide vanes as a kind of cross-flow heat exchanger, the theoretically possible heat exchange action is significantly increased.

Through the heat-transmitting wall that is located between a “cold” and a “hot” venting passage, the cold air can be heated with energy that is removed from the hot air through the wall and the hot air is cooled, depending on in which direction the heat exchange is to be realized. The heat transmission coefficient of the exhaust hood increases because of the parallel conveying stretch. For increasing the heat exchange action, a plurality of air guiding passages can be provided that are arranged adjacent to each other and that, across the common walls and their surfaces, can exchange energy. In order to enable heat transfer, at least some of the guide vanes in the area of the second fan wheel must be embodied as a cavity in order to enable a separate cross-over guiding of the air flows past each other. To which degree, and if at all, the guide vanes in the area of the first fan wheel are embodied as a cavity depends on where the external air is to exit from the exhaust hood and which surfaces are to be utilized for heat transfer. The greater the surface areas available for heat transfer, the more heat can thus be exchanged between the air flows that cross each other.

With the inventive utilization of the guide vanes in the exhaust hood as venting passages, it is possible to dispose the venting passages correlated with first and second fan wheels parallel and adjacent to each other within the exhaust hood without additional deflection means having to be provided. Because of the minimal flow direction deflections, the venting passages create a comparatively low counterpressure so that the energy consumption for the operation of the fan wheels for generating a certain air conveying quantity will decrease.

Moreover, it is possible to design the fan wheels and the components of the venting passages so as to be easily removable so that, for example, for cleaning purposes, they can be removed quickly. It is advantageous to design the components with regard to their dimensions such that they can be fitted into a basket of a conventional dishwasher.

In accordance with one embodiment of the invention, the venting passages for room air discharge and external air supply are arranged annularly and externally about the fan wheels; the venting passages correlated with the first fan wheel have a height that extends into the area of the second fan wheel but have at the fan wheel side only one opening relative to the first fan wheel, and the venting passages correlated with the second fan wheel have a height that extends into the area of the first fan wheel but have at the fan wheel side only one opening relative to the second fan wheel. By extending the venting passages from the area of the first fan wheel into the area of the second fan wheel and vice versa, the surface area available for heat exchange and thus the quantity of the heat that is exchangeable within the exhaust hood is increased.

According to one embodiment of the invention the first and the second fan wheels are separated from each other by a partition that is arranged between them and that separates the correlated air flows from each other. The partition enables an optimization of the respective air flows in the area of the respective fan wheels. By a single partition the dimensions of the exhaust hood according to the invention can be kept compact. Moreover, a single partition also enables an excellent energy exchange between “hot” and “cold” air in the area of the fan wheels.

According to one embodiment of the invention, at least the walls of the venting passages correlated with the first fan wheel have an extension that is curved in radial direction toward the fan wheel. Because of the curvature of the venting passage in a direction radial relative to the fan wheel the air flow is deflected. The defection, when the guide vanes of the fan wheels are designed appropriately, can lead to slowing of the airflow with simultaneous increase of the air pressure. Since the slowing effect leads to a movement path of particles that are moved within the air flow and that have a relative density that is different from that of air that differs from the flow path of the air that is passing through this area, it is possible to utilize the walls of the venting passage in order to catch the particles moved within the air flow, for example, oils or grease from cooking vapors, in that they collide with the surface of the wall and adhere thereto until they are removed in a later cleaning action. Because of the separation of particles in an area directly adjoining the transition area from a fan wheel to the venting passage positioned downstream, the particles are caught in a zone that is close to the fan wheels and therefore still in an area that is easily accessible, in particular, when the fan wheels, or at least one of the fan wheels, is arranged directly behind or in immediate vicinity to the intake opening of the exhaust hood. Because of the curvature of the guide vanes in radial direction, the surface area that is available for the heat exchange is also enlarged because the walls extending in radial direction have a greater length and thus surface area.

According to one embodiment of the invention, the venting passages that are correlated with the first fan wheel open into an annular discharge opening and the inner wall of the discharge opening delimits a receiving opening from where the incoming external air can be supplied to the venting passages correlated with the second fan wheel. The annular discharge opening distributes and makes uniform the air flows coming in from the individual venting passages across the entire available space and guides in this way the airflows in a uniform flow into an exhaust pipe. The outer wall of the annular discharge opening can have a bell shape matched to the flow conditions within the interior. A bell shape is in particular expedient when the exhaust pipe into which the exhaust flow is introduced has a reduced cross-section in comparison to the exhaust hood in the area of the second fan wheel. Since the inner wall at the same time separates the exhaust flow from the incoming flow, in this transition area heat can be transferred effectively. Moreover, the space that is required for partitions is limited to a minimum. Partitions between the incoming flow and the exhaust flow are required only in the area in which the exhaust flow is to be bridged in the effective area of the second fan wheel that is driving the incoming flow.

According to one embodiment of the invention, the first and second fan wheels have an at least approximately identical air conveying volume. By means of the at least approximately identical air conveying volume, it is avoided that underpressure or overpressure states are generated in the vented building in case of extended operation of the exhaust hood. In this way, it is technically precluded that, for example, flue gases of a heating system are sucked in by underpressure into the building. Failure-prone contact switches on windows that monitor a tilted position for venting purposes are no longer required because the exhaust hood is technically designed such that identical, or at least approximately identical, incoming and exhaust flows are produced.

According to one embodiment of the invention, the first and the second fan wheels are arranged on a common shaft. According to a further embodiment of the invention, the first and the second fan wheels can be driven by a common drive motor. Because of this arrangement the exhaust hood can be operated such that only a single drive motor is required when the vanes of the first and second fan wheels convey in opposite directions. Mounting and removal of the fan wheels, for example, for cleaning purposes, is simplified because the fan wheels are a single unit.

According to one embodiment of the invention, the first fan wheel sucks in the incoming room air, forces it into the venting passages correlated with the first fan wheel, wherein the room air can be guided from the venting passages into the discharge opening, and the second fan wheel sucks in the incoming external air, forces it into the venting passages correlated with the second fan wheel, wherein the external air can be guided from the venting passages in a direction that laterally is remote from the rotation axis of the fan wheels. With this configuration the space adjacent to the fan wheels is utilized in order to guide the air flows past the fan wheels. In this connection, the partitions between the incoming and exhaust flows are utilized in order to transfer heat in a desired direction.

According to one embodiment of the invention, an air guiding pipe with a pipe-in-pipe air guiding action can be connected to the exhaust hood. The pipe-in-pipe guiding action makes it possible to utilize the length of the conveying stretch across which the air guiding pipe extends also for transfer of heat.

According to one embodiment of the invention, the venting passages correlated with the first and/or second fan wheel are formed by one or several shaped parts that are removable easily from the exhaust hood. With appropriate molds, the shaped parts can be produced in a simple way even with difficult geometries, for example, from plastic material. Also, locking and/or form-fit connections for connecting a shaped part with the remainder of the exhaust hood can be provided in order to be able to mount and remove the shaped part without a tool, for example, for cleaning purposes.

According to one embodiment of the invention, at least one fan wheel is designed as a shaped part that is easily removable from the exhaust hood. In this connection it holds true also that, with appropriate molds, the shaped parts can be easily produced even with difficult geometries, for example, from plastic material. Also, locking and/or form-fit connections for connecting a shaped part with the remainder of the exhaust hood can be provided in order to be able to mount and remove the shaped part without a tool, for example, for cleaning purposes.

It is expressly noted that the invention according to claim 1 can be combined in any way with individual or several of the afore described embodiments inasmuch as no technical obstacles exist that cannot be overcome.

Further advantageous modifications and embodiments of the invention can be taken from the following objective description, the drawings, and the features of the dependent claims.

The invention will be explained in more detail with the aid of an embodiment. It is shown in:

FIG. 1: a schematic cross-section of an exhaust hood;

FIG. 2: a view of the fan wheels;

FIG. 3: a schematic view of the guide vanes.

In FIG. 1 an exhaust hood 2 is shown in a schematic cross-section view in which the first fan wheel 4 and the second fan wheel 6 can be seen. Externally on the fan wheels 4, 6 guide vanes 8 are arranged. The room air is sucked in by the first fan wheel 4 through an intake opening 10, is accelerated, and is then blown through the openings 12 correlated with the first fan wheel 4 into the venting passages that are laterally delimited by the guide vanes 8. In the area of the guide vanes 8 the room air that has been blown into the venting passages, as indicated by the arrows, flows about the second fan wheel 6.

The external air is sucked in by the second fan wheel 6 through the supply passage 12 and is then blown through the openings 16 correlated with the second fan wheel 6, as indicated also by the arrows, into the venting passages laterally delimited by the guide vanes 8. Since the first fan wheel 4 is separated from the second fan wheel 6 by a partition 18, the respective air flows cannot mix with each other in the area of the fan wheels 4, 6. In the embodiment, the external air is guided through the venting passages into an area that is lateral relative to the first fan wheel 4 where it can enter the room through discharge openings.

The venting passages that are guided from the first fan wheel 4 about the second fan wheel 6 are closed relative to the second fan wheel 6, as indicated in FIG. 1 by the arrows illustrated in dashed lines in this area. The venting passages that are guided from the second fan wheel 6 about the first fan wheel 4 are closed relative to the first fan wheel 4 which in this area is indicated also by the arrows that extend in dashed line. In the section view illustrated in FIG. 1, the venting passages in the area of the fan wheels 4, 6 are illustrated displaced relative to each other in order to be able to illustrate the air inlet through the openings 12, 16 into the venting passages.

The room air that passes through the venting passages after it has passed the area of the second fan wheel 6 reaches the area of an annular discharge opening 20 from where the room air passes into the exhaust pipe 22. In the embodiment, the exhaust pipe 22 and the supply passage 14 are shown as a pipe-in-pipe air guiding system in which the conveying stretch can be used additionally for heat exchange between the incoming external air and the outflowing room air by means of the inner wall 24. The inner wall 24 extends into the area of the discharge opening 20 where it delimits the latter relative to the interior and where it opens into the receiving opening 26 for receiving the external air in the area of the second fan wheel 6.

In the area of the two fan wheels 4, 6 a drive motor 28 is provided having a drive shaft that, according to a preferred embodiment, is coaxial to the axis of rotation of the first and second fan wheels 4, 6. By one drive motor 28 both fan wheels 4, 6 can thus be driven. In this way, it is possible in a simple way to ensure also an at least approximately identical conveying performance of the two fan wheels 4, 6 without this requiring a synchronization of two drive motors for differently adjustable rotary speeds of the fan wheels.

FIG. 2 shows a view of a combined fan wheel 4, 6. The first and second fan wheels 4, 6 according to one embodiment of the invention can also be formed as a single component between which, by retrofitting, advantageously only the partition 18 has been introduced. The rotating fan wheels 4, 6 suck in the room air and external air from the interior and force it by means of the fan blades 30 outwardly into the area of the guide vans.

In FIG. 3 the guide vanes 8 are illustrated in a schematic view. The upper guide vanes 8 a are correlated with the second fan wheel 6 and separated by the partition 18 from the guide vanes 8 b correlated with the first fan wheel 4. The guide vanes 8 a, 8 b are displaced relative to each other by half a spacing of a guide vane 8 relative to a neighboring one. By an arrow it is illustrated how an airflow exiting from the first fan wheel 4 passes through an opening 12 into the venting passage between two neighboring guide vanes 8 a, is deflected upwardly, and is then guided in upward direction through a cavity 32 that is formed in an upper guide vane 8 b. By the displacement of the upper relative to the lower guide vanes 8 a, 8 b, the air flow that enters the lower venting passage can pass into the cavity 32 arranged above. Through the surface 34 of the correlated guide vane 8 b the air flow that is exiting from the first fan wheel 4 and is illustrated in FIG. 3 by the arrow can exchange heat with the air flow that is passing from the second fan wheel 6 into the venting passages between the guide vanes 8 b. The surfaces 34 are not only located on the sides of the guide vanes 8 a, 8 b that are facing the fan wheels 4, 6 but also on the sides that are facing away because they also delimit one side of a venting passage. In this way, for a larger number of guide elements 8 this results in a large surface area available for heat exchange between the respective airflows.

In FIG. 3 the arrow indicates not only the heat exchange in the area of the guide vanes 8 b but, with the aid of the visible openings in the partition 18 it is apparent that an air flow generated by the fan wheel 6 also can enter the guide vanes 8 a that are provided with a cavity 32 and can use its surfaces as heat exchange surfaces. The heat exchange is then realized not only in the dashed upper area of the arrow that symbolizes the air flow but also in the lower area in which the air flow is indicated by the solid arrow.

The invention is not limited to the afore described embodiment but can be modified and adjusted to a concrete application situation by a person of skill in the art in a way that appears suitable to that person. 

1-12. (canceled)
 13. An exhaust hood comprising: a first fan wheel sucking in and transporting away room air; a second fan wheel sucking in external air and arranged axially displaced relative to the first fan wheel; guide vanes arranged externally about the first and second fan wheels; wherein the guide vanes are embodied as a cavity and form venting passages; wherein a first air flow exiting from the first fan wheel and a second air flow exiting from the second fan wheel are guided past each other, separate from each other, through the guide vanes and are directionally deflected by the guide vanes; wherein walls of the guide vanes form a surface for heat exchange between the first and second air flows.
 14. The exhaust hood according to claim 13, wherein: the venting passages for the first air flow effecting room air discharge and the venting passages for the second air flow effecting external air supply are arranged annularly externally about the first and second fan wheels; the venting passages correlated with the first fan wheel have a height that extends into an area of the second fan wheel but have only one opening relative to the first fan wheel; the venting passages correlated with the second fan wheel have a height that extends into the area of the first fan wheel but have only one opening relative to the second fan wheel.
 15. The exhaust hood according to claim 13, further comprising a partition arranged between the first and second fan wheels so that the first and second fan wheels are separated from each other, wherein the partition separates the first and second air flows from each other.
 16. The exhaust hood according to claim 13, wherein at least the walls of the venting passages correlated with the first fan wheel have an extension that is curved in radial direction toward the first fan wheel.
 17. The exhaust hood according to claim 13, comprising an annular discharge opening having an inner wall, wherein the venting passages correlated with the first fan wheel open into the annular discharge opening, wherein the inner wall of the discharge opening delimits a receiving opening from where the external air sucked in by the second fan wheel is guided to the venting passages correlated with the second fan wheel.
 18. The exhaust hood according to claim 17, wherein: the first fan wheel sucks in the room air and forces the room air into the venting passages correlated with the first fan wheel, wherein the room air is guided from the venting passages into the discharge opening; and the second fan wheel sucks in the external air and forces the external air into the venting passages correlated with the second fan wheel, wherein the external air is guided from the venting passages in a direction laterally away from the rotational axis of the fan wheels.
 19. The exhaust hood according to claim 17, further comprising a pipe-in-pipe air guiding system connected to the annular discharge opening.
 20. The exhaust hood according to claim 13, wherein the venting passages correlated with the first and/or second fan wheels are one or more shaped parts easily removable from the exhaust hood.
 21. The exhaust hood according to claim 13, wherein at least one of the first and second fan wheels is a shaped part that is easily removable from the exhaust hood.
 22. The exhaust hood according to claim 13, wherein the first and second fan wheels have an at least approximately identical air conveying volume.
 23. The exhaust hood according to claim 13, comprising a common shaft on which the first and second fan wheels are arranged.
 24. The exhaust hood according to claim 13, comprising a common drive motor wherein the first and second fan wheels are driven by the common drive motor. 